Power distribution centers (PDCs) are commonly used in automotive vehicles to simplify electrical system wiring by eliminating multi-branch wiring and consolidating fuses, relays, and other electrical components in a single location. A PDC typically comprises a plastic case having receptacles on its upper surface for receiving the electrical components and containing bus bars or other conductive means for interconnecting and supplying power to the various components. Electrical connectors are also disposed on the upper surface of the PDC, these mating with the connectors which terminate wire harnesses to interconnect the circuitry of the PDC with various vehicle electrical systems and devices elsewhere in the vehicle. Some of the wire harness connectors are quite large. A typical engine harness connector, for example, may contain approximately 45 terminals and measure five centimeters by six centimeters. A large wiring harness connector is usually secured to its mating connector on the PDC by means of a nut-and-bolt connection in which captive bolt passes through the center of the wiring harness connector and is threaded into a nut molded into the mating connector. Tightening the bolt urges the two connectors into electrical contact with one another, an operation that may otherwise be difficult to achieve due to the large insertion forces that accompany connectors with large numbers of terminals.
PDCs are often located within the engine compartment of the vehicle, and so are fitted with upper and lower housings to protect the PDC from contaminants such as dirt, water and other debris that may be present. The lower housing is typically bolted or otherwise secured to some structure within the engine compartment and thus serves as a mounting bracket for the PDC. The upper housing is usually removable to provide access to the circuit components on the PDC.
As the number of vehicle electrical systems has increased, it has become necessary in many cases to connect wire harnesses to the lower surface of the PDC. It is the general practice in the automotive industry to assemble the PDC prior to shipping it to a vehicle assembly plant for installation in the vehicle. At this point the necessary wire harness connections are made to the PDC. Because of the limited amount of space in most engine compartments, it may be difficult or impossible to reach the bottom of the PDC and make such connections after the PDC has been secured in place. If the connections must be made to the bottom of the PDC prior to securing it in the engine compartment, the assembly person must hold the PDC upside down, position the wire harness connector in alignment with the mating connector, and drive the captive bolt into engagement with the nut. This procedure is very awkward and time consuming, and increases the chance of accidental damage to the components.
An alternative assembly method is to connect the wire harnesses to the lower surface of the PDC prior to shipment to the final assembly plant. This is not desirable because the resulting assembly is quite large and cumbersome, and so is difficult to handle and install in the vehicle.